1. Technical Field
The present invention relates to a liquid ejecting apparatus, a head unit, and a method of controlling the liquid ejecting apparatus.
2. Related Art
In ink jet printers that print images or documents by ejecting ink, piezoelectric elements (for example, piezo elements) are known to be used. The piezoelectric elements are installed to correspond to a plurality of nozzles in head units, respectively, and are driven according to driving signals so that a predetermined amount of ink (liquid) is ejected from the nozzles at predetermined timings and dots are formed. Since the piezoelectric elements are capacitive loads as in capacitors from the electric viewpoint, sufficient currents are necessarily supplied in order to operate the piezoelectric elements of the respective nozzles.
For this reason, driving signals amplified by amplification circuits are configured to be supplied to the head units so that the piezoelectric elements are driven. As the amplification circuits, types of circuits (linear amplification; see JP-A-2009-190287) performing current amplification on source signals before amplification into class AB or the like can be exemplified. However, since power consumption is large and energy efficiency is poor in the linear amplification, class D amplification has recently been proposed as well (see JP-A-2010-114711).
On the other hand, in printing apparatuses, high-speed printing or high-resolution printing have recently been requested strongly. In order to realize the high-speed printing, the number of dots formable per unit time may be increased. In order to realize the high-resolution printing, the amount of ink ejected from the nozzles may be set to be small and the number of dots formable per unit area may be increased. That is, in order to realize the high-speed printing and the high-resolution printing, the number of dots formable per unit time and unit area may be increased. In order to increase the number of dots, a method of increasing an ink ejection frequency is adopted.
Incidentally, in order to increase the ink ejection frequency, it is necessary to increase the frequency of a driving signal supplied to the piezoelectric elements. In order to increase the frequency of the driving signal, decrease an influence of residual vibration or the like, and perform reliable ejection, it is necessary to increase a switching frequency of class D amplification.
However, when the switching frequency is increased, a loss by switching becomes large. Eventually, energy efficiency in the class D amplification may be less than energy efficiency by linear amplification, and thus high energy efficiency which is the advantage of the class D amplification may not be realized.
Further, when the switching in the class D amplification is performed at a high frequency, a problem of an erroneous operation by noise, heat generation resulting from a switching loss, or the like occurs.
Thus, when the switching frequency of the class D amplification is increased in order to increase the frequency of the driving signal used to drive the piezoelectric elements, many problems may occur.